The present application claims priority to Japanese Patent Application No. 2001-263635 filed in the Japanese Patent Office on Aug. 31, 2001 and Japanese Patent Application No. 2002-223133 filed in the Japanese Patent Office on Jul. 31, 2002, the disclosures of which are hereby incorporated by reference herein in their entirety.
1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, a printer, or other similar image forming apparatus, and more particularly, to an image forming apparatus that forms stable and high quality images while improving the durability of an electrophotographic photoreceptor.
2. Discussion of the Background
As an electrophotographic photoreceptor (hereafter referred to as a xe2x80x9cphotoreceptorxe2x80x9d) for use in an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, a printer, or other similar image forming apparatus, an organic photoreceptor has been used because of its low cost, the ease of mass producing it, and because it is non-polluting. However, as compared to an inorganic photoreceptor, an organic photoreceptor has disadvantages such as decreased durability and reduced abrasion resistance. Recently, a need has existed for a photoreceptor having a small diameter because there is a demand for downsizing electrophotographic systems. Therefore, there is a demand for a photoreceptor having good durability against abrasion that increases in proportion to the number of copies. Thus, mechanical durability, which typically means abrasion resistance, is in strong demand.
Japanese Laid-open Patent Publication No. 1-170951 describes a method for improving abrasion resistance of an organic photoreceptor whose surface includes a protective layer including a filler formed from a metal or a metal oxide. By this background method, a photoreceptor having a high mechanical durability can be obtained. However, in such an organic photoreceptor, the properties of the surface of the photoreceptor may be changed with time, because the surface of the photoreceptor is repeatedly charged with a charging device. As a result, toner of a toner image formed on the photoreceptor tends to adhere to the surface of the photoreceptor, and a transfer efficiency of the toner image formed on the photoreceptor may decrease, thereby causing an inferior image such as a partial omission of a transferred image.
In order to prevent toner from adhering to the surface of the photoreceptor due to the surface property changes of the photoreceptor, a method has been employed in which surface energy of a photoreceptor is decreased by applying a lubricant onto the photoreceptor. As a background method of applying a lubricant onto a photoreceptor, Japanese Laid-open Patent Publication No. 2000-162881 describes a method of applying a lubricant onto a photoreceptor with a lubricant applying member, such as a brush. Further, Japanese Patent No. 2859646 describes a method of applying a lubricant added to a toner onto a photoreceptor. By applying a lubricant onto a surface of a photoreceptor, the surface energy of the photoreceptor is decreased, thereby improving the mechanical durability of the photoreceptor and the transfer efficiency of a toner image, and preventing an occurrence of an inferior image such as a partial omission of a transferred image.
With regard to the application of a lubricant onto a photoreceptor, there are some problems to be addressed. When applying a lubricant onto a photoreceptor with a lubricant applying member such as a brush, a regular maintenance or replacement of the lubricant is required. If a large quantity of lubricant is used in an apparatus to lengthen a maintenance interval, the size and cost of the apparatus increase.
When a lubricant is added to toner and applied onto a photoreceptor, fresh lubricant is applied to the photoreceptor by replacing a toner bottle. Therefore, as compared to the above-described case in which a lubricant is applied onto a photoreceptor with a lubricant applying member, maintenance of the lubricant itself is not required. However, there is a problem that an amount of a lubricant applied onto a photoreceptor depends on an area of a toner image formed on the photoreceptor. Specifically, when a large number of toner images are formed on the photoreceptor and toner of the toner images are transferred onto a transfer material such as a transfer sheet from the photoreceptor, a sufficient amount of lubricants, which are added to the toner, remain and are supplied onto the photoreceptor. However, when a small number of toner images are formed on the photoreceptor, an amount of lubricants supplied onto the photoreceptor decreases accordingly.
According to a first aspect of the present invention, an image forming apparatus includes at least one image carrier configured to carry an electrostatic latent image on a surface of the at least one image carrier, at least one developing device configured to develop the electrostatic latent image with a developer including a toner to which a first lubricant is added to form a toner image on the surface of the at least one image carrier, a lubricant applying device configured to apply a second lubricant onto the surface of the at least one image carrier, a lubricant application amount adjusting device configured to adjust an amount of the second lubricant to be applied onto the surface of the at least one image carrier, and a control device configured to at least control the lubricant application amount adjusting device to adjust the amount of the second lubricant to be applied onto the surface of the at least one image carrier according to an area of the toner image formed on the surface of the at least one image carrier.
According to another aspect of the present invention, an image forming method includes the steps of carrying an electrostatic latent image on a surface of at least one image carrier, developing the electrostatic latent image with a developer including a toner to which a first lubricant is added to form a toner image on the surface of the at least one image carrier, applying a second lubricant onto the surface of the at least one image carrier, and adjusting an amount of the second lubricant to be applied onto the surface of the at least one image carrier according to an area of the toner image formed on the surface of the at least one image carrier.